Radio Frequency (RF) transmissions are becoming widely used in various fields. Because of advances in semiconductor technologies, an arbitrary waveform generator (AWG) now features 10G samples per second or more, which allows the AWG to generate a microwave signal directly without up-converters. For example, the AWG7122C arbitrary waveform generator, manufactured by Tektronix, Inc., Beaverton, Oreg., has a maximum sampling rate of 24 Giga-sample per second. One of applications of such an AWG is the generation of a radar signal. A typical radar signal is an RF (radio frequency) pulse train as shown in FIG. 1.
An ultra-high speed sampling rate is required to generate microwave signals, which makes the waveform data very large thus requiring a large size of a waveform memory to store data. For instance, 10G words of waveform memory are required to generate one second waveform at 10 G sample/second.
FIG. 2A is an example of a simplified radar signal. Each trapezoid of P1 to P4 represents a set of RF pulses and each of T1 to T4 shows a dead time. Note that each T1 to T4 dead time has no signal but the timing information of these components is very important because the range information on a target object will be included in the reflected signal from the object. FIG. 2B is a zoomed version of the simplified radar signal of FIG. 2A. FIG. 2B shows that each RF component, such as one of P1 to P4, includes a plurality of pulses and is defined by the duration of the pulses.
FIG. 3 is a block diagram of a conventional waveform generation circuit used in an AWG. Waveform data such as radar signal data are stored in waveform memory 52 and provided to a digital to analog converter (DAC) 54 under sequence control of a sequencer 50 including a sequence memory 48. The DAC 54 receives a sampling clock Fs from a clock generator 56 that defines the sampling rate. The DAC 54 provides an analog waveform signal to an output circuit 58 that has re-construction filters, amplifiers and attenuators to obtain an analog signal having desired bandwidth and amplitude. A CPU (not shown) controls operation of the blocks.
The simplified radar signal of FIG. 2A may be divided into some components that are stored as digital data in a waveform memory 52 of the waveform generation circuit 31. FIG. 4 shows the components of the simplified radar signal wherein the RF components P1 to P4 of FIG. 2 are left as they are in the memory 52 but the dead time components of T1 to T4 are squeezed into ST1 to ST4 components respectively. For example, the dead time components of T1 may be provided by repeating ST1 n1 times, or T1=ST1*n1.
FIG. 5 is an example of a sequence table 1 based on the example of FIG. 4. The sequence memory 48 store the sequence table 1 and the sequencer 50 controls the waveform memory 52 to provide waveform data “*.wfm” to the DAC 54 according to the sequence table 1. This method uses the waveform memory even when the RF pulses are not generated and then requires a large memory space.